<meta charset="utf-8">
<!-- <script src="main.js"></script> -->
<script src="https://unpkg.com/vue/dist/vue.js"></script>
<style>
  

</style>
<body>
    

    <div id="app">
        
      <input type="text"  v-model="n1">
      <select v-model="sel">
        <option value="+">+</option>
        <option value="-">-</option>
        <option value="*">*</option>
        <option value="/">/</option>
      </select>
      <input type="text" v-model="n2">
      <button @click="calc">=</button>
      <input type="text" v-model="result">

    </div>
    </body>


    <script>
        var vm = new Vue({
          el: '#app',
          data: {
            n1: 0,
            n2: 0,
            sel: '+',
            result: 0,
            
          },
          methods: {
            calc() {
              var a = parseInt(this.n1)+ this.sel + parseInt(this.n2)
              this.result = eval(a)
            }
        
          },


        });
    </script>